Electrical safety switching device



Jan. 14, 1941. P. w. DUNN ELECTRICAL SAFETY SWITCHING DEVICE Filed Aug. 25, 1938 I5 Sheets-Sheet l Willi.

INVENTOR w WwW ATTYS.

Jan. 14, 1941.

P. W. DUNN ELECTRICAL SAFETY SWITCHING DEVICE Filed Aug. 23, 1938 3 Sheets-Sheet 2 R O N E V N RW. DUNN Jan. 14, 1941. P. w. DUNN 2,228,817

ELECTRICAL SAFETY SWITCHING D EVICE Filed Aug. 23, 1938 3 Sheets-Sheet 3 INVENTOR PW. D u N N v W'WPATTYS,

Patented Jan. 14, 1941 UNITED STATES PATENT OFFICE Application August 23, 1938, Serial No. 226,368 In Great Britain September 2, 1937 6 Claims.

This invention relates to electrical safety switching devices for use on vehicle or aircraft. The invention is concerned with such safety switching devices of the kind in which the displacement by a shock of a quantity of mercury from a receptacle in which it is normally contained is employed to make or break an electrical circuit including contacts with which the mercury 00- operates.

10 According to the present invention there is provided a safety switching device of the aforesaid kind comprising a receptacle for a small quantity of mercury, a second receptacle connected to the first by means of one or more narrow passages such that the mercury does not freely flow therethrough and a plurality of electric contacts arranged close to one another in the second receptacle. When the device is subjected to a violent shock the mercury or a portion of it is thrown through the narrow passage or passages into the second receptacle and shortcircuits the electric contacts therein.

The invention further comprises a safety switching device as aforesaid in which the receptacle for the mercury comprises a cup-like part having an outwardly flared opening and a cover part of substantially complementary shape positioned within the flared opening with small clearance to form the passage for the mercury. It is convenient to mount the device with the cup-like part of the mercury receptacle normally in an upright position and the inner surface of the cover part is conveniently of dished form to receive the mercury when the device is inverted.

A further feature of the mercury receptacle consists in the provision of a peripheral, inwardly directed deflecting shoulder in the cup-like part below the flared opening. The purpose of this shoulder is to receive and temporarily retain 4D the mercury from the cup as the device is turned over so that when approximately in the inverted position any mercury flowing over the shoulder will fall clear of the passage into the dish-shaped cover part. A baflie may also be conveniently provided in the lower portion of the cup-like part to cause mercury leaving the cup to pass close to the wall of the latter and provision of such a baffle renders the device less sensitive when in the upright position.

According to a further feature of the invention the inner walls of the second receptacle diverging from the outlet of the passage or passages will terminate at a plurality of peripheral contacts at the outer extremity of these walls. In one construction, the second receptacle comprises two opposed end walls having inwardly projecting domed or conical surfaces and the outlet of the passage or passages opens into the narrowest part of the space bounded by these walls. Thus, in any position of the device mercury thrown through the passage or passages into the second receptacle will travel directly to the peripheral contacts aforesaid under the action of gravity. Another featureof the invention consists in. that the receptacle is closed by an outer wall bridging m the space between the peripheral margins of the two end walls, which peripheral wall has an inwardly projecting domed or conical inner surface so that in no circumstances will mercury in the second receptacle come to rest upon this peripheral wall but will flow to the contacts at the periphery of one or the other of the end walls.

In one construction the end walls and the peripheral walls of the second receptacle as constructed as aforesaid are formed, as to their in- 20 her surfaces, of conducting material to constitute the electric contacts and these walls are secured together with an interposed thin layer of insulating material between them. In operation of the device, the mercury serves to bridge this thin layer of insulating material. Instead of employing two contacts at the periphery of each side wall, a larger number of contacts may be employed and according to another construction of the device there is provided a plurality of inner ring-like insulated contacts carried by the peripheral Wall at opposite ends thereof and cooperating with other electric contacts constituted or carried by the adjacent end walls.

In one preferred construction end cover-like 35 parts for the mercury receptacle are mounted in a housing fitting in openings in the opposed end walls of the second receptacle and constituting a coupling member securing the walls of this latter receptacle in the assembled position. The cup-like and cover parts of the mercury receptacle may be adjustably interconnected for varying the width of the mercury passage.

In another construction of the safety switch- 45 ing device according to the invention having the inner walls of the second receptacle diverging from the outlet of the mercury passage or passages with peripheral contacts at the outer extremities of these walls, this second receptacle is 50 of conical or similar taperin form and has a mercury receiving well at its small end and additional electric contacts in the well adapted to be bridged by the mercury. Conveniently, in this construction the cup-like and cover parts of the 55 Cal mercury receptacle are mounted respectively on opposite sides of the second receptacle.

Several specific embodiments of the invention are illustrated by way of example in the accompanying drawings, in which:

Figure 1 is a plan of one construction of safety switch;

F'gure 2 is a section on line 2-2 of Figure Figure 3 is a cross-section similar to Figure 2 showing another construction of the device;

Figure 4 is a cross-section of an alternative construction of mercury receptacle;

Figure 5 is a cross-section of another construction of safety switch according to the invention;

Figure 6 is a section on line 6-3 of Figure 5, and

Figure 7 is a or ss-section of an alternative construction of mercury receptacle.

Like references indicate like parts in the several figures of the drawings.

Referring to Figures 1 and 2 of he drawings, ahousing i9 is formed with a cylindrical chamber H in which the two receptacles are detachably mounted. Bearing against a shoulder ii. at one end of this chamber, there is a contact ring it insulated from the housing and a metallic conical member l4 constituting one of the end walls of the second or contact receptacle is formed with a flange l5 mounted against the ring l3. At the other side of the flange there is a thin ring 55 of insulating material such as mica. A circular peripheral wall I! for the contact chamber is formed of insulating material and has a metallic layer l8 on its inner side with end faces :9, one of which bears on the insulating ring it. The inner metallic surface of this wall is inwardly domed in cross-section.

A second metallic end wall similar to the end wall !4 has a flange 2l bearing against a thin ring of insulating material 22 similar to the insulating ring l3 interposed between this flange the adjacent end face l9 of the peripheral wall ll. he complete assembly for the contact receptacle is secured in position by a lock ring 23 screwthreaded into the housing I!) and insulated from the end wall 20.

The mercury receptacle comprises a cup-like part 2 having a well 24a and a separately formed ring iii providing an inwardly directed annular shoulder and above this shoulder an outwardly flared opening 23. A cover part 21 for this receptacle is of conical form complementary with the flared opening 26 of the cup-like part and the two parts are arranged with a small gap 39 constituting the passage for the mercury. The inner surface ill of the cover part is of concave form.

The cup-like part of the mercury receptacle is carried in a metallic tubular housing 29 and is held in position against a shoulder 39 in this housing by means of a disc 3| screwthreaded in the housing. The cover part 2'! of the mercury receptacle is secured to an end member 32 screwthreaded in the opposite end of the housing 29 so that by rotating this end member 32 the width of the passage between the flared opening of the cup-like part and the complementary conical surface of the cover part can be closely adjusted to the required extent. The width of the passage depends on various factors including the conditions of use of the device and the amount of mercury employed and generally will be less than 33 of an inch. The end member 32 has a screw-threaded part 33 carrying a nut 34 by means of which a locking member 35 may be frictionally held against the end of the housing 29.

The mercury receptacle thus formed as a unit is located in central h .es in the two end walls It and 29 of the contact chamber. It is formed with a flange bearing on the end wall 29 and is secured in position by means of a nut 3'! screwthreaded on the housing 29 and bearing on the other end wall 14. The housing 29 is formed with a plurality of apertures 39 spaced around the outlet from the passage 39 so as to permit mercury thrown from the cup-like part 24 to run into the outer contact receptacle.

The inner conducting wall l8 constitutes one contact of the switch and is in electrical connection with a sleeve 49. A stud H engaging with a contact strip 42 is screwtineaded into a sleeve ll} and on the strip 42 there is mounted a plurality of terminals 43 in a junction box 44. The end walls l4 and 20 which alternatively constitute the other terminals of the switch are electrically connected by the housing 29 and the contact ring l3, which is in electrical contact with the flange 15 of the end wall 1:1, is formed with an extension 45 in the junction box 44 carrying a terminal 49.

Should the device be turned on one side as may happen when a device is fitted to an aircraft, the mercury is prevented from reaching the passage 39 by means of the shoulder 25. If, by further turning movement, the device should be inverted the mercury flows over the shoulder 23 into the cavity 28 again without passing down the passage 39.

The device is normally mounted in the position shown in Figure 2 with a small quantity of mercury indicated at GT in the mercury receptacle. Under normal operation of the vehicle or aircraft to which it is attached, the mercury remains in its receptacle, but should a violent shock occur, the mercury is thrown through the passage 39 into the contact receptacle and by reason of the construction of this latter receptacle for any position of the device when the shock occurs, the mercury must fiow towards the inner edge of one of the insulating rings It, 22 so as to bridge this insulating ring and make contact between the conducting wall l9, 13 nd either of the conducting end walls M or 29. Since the contacts of the device are separated by only a very thin insula tion only a small quantity of mercury serves to short-circuit the contacts.

The width of the mercury passage 39 is such that owing to the surface tension of the mercury, the mercury will not readily flow through the passage when gently reaching the inner end of the passage for instance as the device is turned over. The shoulder 25 serves to deflect the mercury from the passage 39 so as to ensure that the mercury does not flow to the passage except when the device is subjected to a sharp shock, throwing the mercury about the receptacle and forcing it through the passage.

In the construction shown in Figure 2, there are in effect two contacts because the end walls l4 and 20 are electrically connected together by the housing 29 of the mercury receptacle. Alternatively, a. larger number of contacts may be employed and in Figure 3 there is shown a construction having three independent contacts. Referring to Figure 3, the peripera] wall I! of insulating material is provided at its ends with contact rings and SI respectively secured in position by means of rivets 52 passing through the material of the wall ll. At the outer sides of these contact rings there are other contact rings 53 and 54 respectively insulated from the others by a thin layer 55 of insulating material such as mica. The contact rings 53 and 54 are secured in position by means of rivets 56 which are insulated from the contact rings 58 and Therivets 52 serve as an electrical connection for the inner contact rings 50, 5| and the rivets 56 similarly electrically connect the outer contact rings 53 and 54.

In this construction the flange I5 of the end wall I4, separated from the contact ring 54 by a thin ring of insulating material I6 as in the preceding construction, is in this case of reduced diameter and an insulating ring 51 carrying annular contacts 58 and 59 is interposed between the flange |5 and the flange l2 of the housing. The annular contact 58 abuts against the contact ring 54 and the annular contact 59 abuts the flange I5 and the two annular contacts 58 and 59 are connected by leads 60 and BI to terminals 62 and 63 respectively. The inner contact rings 50 and 5| are connected to another terminal 84 by means of a brush 85 carried by the terminal in the casing I8 and engaging a stud 66 screwthreaded in one of the rivets 52. Thus, in operation of this construction of the device the mercury when spilled from the mercury container must flow into contact with one of the end walls I4 and 28 and make contact between the end wall and either of the rings 58 and 5| and also either of the rings 53 and 54.

Instead of constructing the mercury container with provisions for adjusting the width of the outlet passage 39, it may in some circumstances be preferable to form this receptacle with a passage of fixed width. For example, as shown in Figure 4, the cover part 21 of the receptacle is formed with a flange 41 engaging a shoulder 48 on the housing 29 to determine the width of the passage 39 and the cover part 21 is retained in position by a plug 48 screwthreaded into the housing.

In the construction shown in Figures 5 and 6 the mercury receptacle is constructed in two parts 18 and II screwthreaded into the wall of the second receptacle indicated at I2. The cuplike part ID has a well 24a, an inwardly directed flange 25 and a flared opening 26, as in the preceding construction, and the cover part II is also formed with a conical part spaced from the flared opening 26 to provide the mercury passage 39 and the inner concave wall 28. In this construction the shoulder 25 is substantially horizontal but it may be undercut as shown in Figure 2.

The second or contact receptacle surrounds the outlet of the mercury passage 39. The receptacle has a substantially rectangular inner wall 13 joining with contiguous walls 14 diverging and merging smoothly at a circular end wall I5 at one side of the mercury receptacle. The receptacle 12 comprises ring parts 16 and 11 of conducting material, the outer surface of the latter being separated from the outer wall I5 by a thin layer I8 of insulating material such as mica. The ring part I1, the end wall I5 and the interposed insulating layer I8 are secured in position by means of a cap 19 screwthreaded on the outer side of the receptacle 12, the end wall I5 being insulated from the ring 19 by an interposed insulating member 80.

At the opposite end of the said receptacle. 12, an end plate 8| of conducting material is secured thereto by screws 82 engaging in the ring member 18 and carries a plug 83 of insulating material in which is mounted a contact stud 84 having an inner head 85 positioned in a well 86 formed partly and bounded at least partly, by a wall 81 of the end plate 8|. The stud 84 is bridged to the stud 88 by a metal strap 89 and one terminal of the switch is provided at 98 on the stud 84 and the other at 9| on the fixing ring 19. Thus, in operation of construction of the device a violent shock throws the mercury through the narrow passage 39 into the second receptacle which either flows towards the end wall I5 to bridge the insulating material between this wall and the conducting ring member 11 which is in electrical connection with the terminal 9| or flows to the other end of the receptacle and serves to connect the head 85 of the stud 84 to the. end wall 8| which is also in electrical connection with the terminal 9|.

In some circumstances it may be necessary to render the device less sensitive to vertical shocks than to shocks in other directions. For this purpose, a modified construction of the cup-like part of the mercury receptacle may be employed, for example a construction as shown in Figure 7 and intended for use in the construction of the device illustrated in Figures 5 and 6.

In Figure 7 the cup-like part of the receptacle is formed in two portions 92 and 93 screwthreaded together. The portion 93 has a well 94 for the mercury and above the well there is a bafile 95 having a flange 96 interposed between shoulders and. the two portions 92 and 93 which are screwthreaded together. The inwardly directed shoulder 25 is in this construction undercut at 91 to a pronounced extent and the baflies 95 contain a plurality of passages 98 leading from the periphery of the well 94 to the undercut recess 91. There is also a central vertical opening 99 in the baiile and the top and bottom sides of the baffle are of concave form as shown.

With this construction of mercury receptacle when the device is simply inverted the mercury flows from the well 94 through one or more of the passages 98 into the undercut recess 91 and eventually when the device is completely inverted into theconcavity 28 of the cover part II, which is of the construction shown in Figures 5 and 6, when the device is righted again the mercury flows through the central passage 99 in the baffle back to the well 94. When in the upright position a vertical shock; throws the mercury through the passage 99 in the bafile and through the narrow outlet passage 39 and by reason of the bafiie a considerably greater shock is necessary in this direction than in the case where no baiiie is employed in order to operate this device.

One application of the safety switching device according to the invention, is for short-circuiting the ignition system of the engine in a vehicle or aircraft in the event of an accident. It may alternatively be used to control electrically other devices in a vehicle or aircraft as the result of an unusual shock and, for instance, may be employed automatically to set fire-extinguishing apparatus in operation.

It will be understood that the safety switching device, according to the invention, is not restricted to the specific constructions hereinbefore described. In particular the shape of the mercury well, the form of the inwardly directed flange above the well, the size of the outlet passage for the mercury and the interior baflle, if employed, may be modified in shape according to the conditions under which the device is to operate in a particular case, It will be understood that any convenient means other than that hereinbefore described may be employed for adjusting the width of the mercury passage, such for example as the use of packing shims interposed between the cup-lile and cover parts of the mercury receptacle.

I claim:

1. A safety switching device comprising a receptacle for a small quantity of mercury, a second receptacle connected to the first by at least one narrow passage such that mercury does not fiow freely therethrough, said second receptacle comprising two opposed end walls having inwardly projecting conical surfaces disposed with the narrowest part of the receptacle bounded by said walls at the outlet end of said passage, an outer peripheral wall bridging the space between the peripheral margins of said end walls, which peripheral wall has an inwardly bulging inner urface, and a plurality of peripheral electric contacts arranged close to one another at the outer extremities of said end walls.

2. A safety switching device comprising a receptacle for a small quantity of mercury, a second receptacle connected to the first by at least one narrow passage, such that mercury does not flow freely therethrough, said second receptacle comprising two opposed end walls having inwardly projecting conical surfaces of conducting material disposed with the narrowest part of the receptacle bounded by said walls at the outlet of said passage, an outer peripheral wall having an inwardly bulging inner surface formed of conducting material and a thin layer of insulating material disposed between each of said end walls and said peripheral wall, whereby said end walls and said peripheral wall constitute electric contacts adapted to be connected by mercury.

3. A safety switching device comprising a receptacle for a small quantity of mercury, a second receptacle connected to the first by at least one narrow passage, such that mercury does not flow freely therethrough, said second receptacle comprising two opposed end walls having inwardly projecting conical surfaces of conducting material disposed with the narrowest part of the receptacle bounded by said walls at the outlet end of said passage, an outer peripheral wall having an inwardly bulging inner surface, a plurality of insulated ring-like electric contacts intel-posed between each of said end walls and said peripheral wall, which contacts and said end walls are adapted to be electrically connected by mercury flowing into the said second receptacle.

4. A safety switching device comprising an outer receptacle having two opposed end Walls formed with inwardly projecting conical surfaces, a peripheral wall bridging the space between the peripheral mar'gins of the end Walls and a plurality of electric contacts arranged close to one another at the outer margins of said end walls, a mercury receptacle, said mercury receptacle comprising a cup-like part having a flared opening and a cover part of complementary shape positioned within the flared opening with small clearance to provide a narrow passage for mercury, openings in said end walls at the narrowest part of said outer receptacle between said end walls, and a housing for said mercury receptacle, said housing fitting in and closing said openings with the said narrow passage opening into said outer receptacle, and means in said housing for relatively adjusting said cup-like and cover parts of the mercury receptacle to vary the width of the passage.

5. A safety switching device comprising a receptacle for a small quantity of mercury, 21. second receptacle connected to the first by means of at least one narrow passage, such that mercury does not flow freely therethrough, which second receptacle is of tapered form and comprises a mercury receiving well closing the smaller end of said receptacle, electric contacts in said well, means closing the larger end of said second receptacle and a plurality of peripheral electric contacts at the larger end of said second receptacle.

6. A safety switching device comprising a receptacle for a small quantity of mercury, a second receptacle connected to the first by means of at least one narrow pasage, such that mercury does not flow freely therethrough, which second receptacle is of tapered form and comprises a mercury receiving well closing the smaller end of said receptacle, electric contacts in said well, means closing the larger end of said second receptacle and a plurality of peripheral electric contacts at the larger end of said second receptacle, said receptacle for mercury comprising a cup-like part having an outwardly i'iared opening and a cover part of substantially complementary shape positioned within the flared opening with small clearance to form the said passage for the mercury, which cup-like and cover parts are mounted respectively in opposite sides of said second receptacle with the said passage opening into the latter.

. PERCY WALTER DUNN. 

